Distant reading electromagnetic balance



Dec. 27, 1938. s. E. DAWSON 2,141,175

DISTANT READING ELECTROMAGNETIC'BALANCE Filed March 2, 1934 2 Sheets-Sheet 1 INVENTOR Samuel E. DAWSON ATT R Dec. 27, 1938. 's. E. DAWSON DISTANT READING ELECTROMAGNETIC BALANCE Filed March 2, 1934 2 Sheets-Sheet 2 WIVIM 700.704

INVENTOR BY SAMUEL E DAWSON ATTOENEY AMPLIFIER.

"Patented Dec. 21, 1938 PATENT OFFICE.

DISTANT READING ELECTROMAGNETIC BALAN Samuel E. Dawson, Washington, D. 0.

Application March 2, 1934, Serial No. 713,761

5 Claims.

(Granted under the act of March 3, 1883, as

amended April 30, 1928; 370 O. G. 757) l'his invention relates to automatically controlled distant reading electro-magnetic balances and has, as an object, the accurate measurement of forces at an inaccessible or distant point.

5 My invention comprises an improved method of and apparatus for weighing articles of varying mass for measuring variable forces with practical imvarying accuracy and sensitiveness throughout long periods of extensive use although the apparatus by which the method may be practised may be conveniently portable.

"Weighing methods and apparatus which lack precision and sensitiveness and may not comply with the high requirements of unvarying accuracy and sensitiveness long established by commerce and the penal laws are worse than useless and promotive oi obliquity and fraud.

An object of my invention is to provide a method of and apparatus for weighing which may ac- 26 curately indicate the weight or force measured at a point distant from the Weight or force measured and which weight or force may not be conveniently accessible to the person performing or conr trolling the weighing or measuring operation.

2 Another object of my invention is to provide an improved electro-magnetic balance which may accurately measure throughout long periods of arduous service the amount or" energy of widely variable forces or the mass of widely variable 9i weights.

Another object of my invention is to provide an electro=-magnetic balance in a self-contained, compact, readily portable, highly accurate and a long enduring mechanism forming a part or" an electric circuit.

Another object of this invention is to permit the reading and recording of several relatively widely variable forces acting simultaneously where it would be inconvenient or impossible to maintain equilibrium or to take readings on several balances of the usual type embodying weights or springs.

A further object of this invention is to provide an automatically controlled distant reading 45 electro-magnetic balance having a high ratio of effective pull to weight and practically free from external electrical, magnetic or other variable infiuences including inherent friction.

A still further object of this invention is to 50 provide an electromagnetic balance capable of sensitive accuracy even when functioning while submerged in water or other liquids or gases.

Other objects of the invention will appear more fully hereinafter.

55 The invention consists substantially in the construction, combination, location, and relative arrangement of parts, all as will be more fully here lnafter set forth, as shown in the accompanying drawings, and finally pointed out in the appended claims.

Reference is to be had to the accompanying drawingsiorming a part of this specification, in which like reference characters indicate corresponding parts throughout the several views, and in which: is

Fig. l. is a view in perspective partially in sectlon of the operative element of my invention and,

Fig. 2 is a side elevation of the operative ele= ment together with a diagrammatic showing of its associated electrical circuits.

It is customary, in the testing of models of various kinds, to measure forces by certain wellknown combinations of weights, springs and levers. Equilibrium is maintained by manual 21} shifting of weights or adjustment of springs. Forces are then read off directly, at the apparatus, by observers. There are many variations of these practices, some of them semior fully automatic, made possible by recent developments, in the de- 25 sign of these instruments. The mechanical types usually have heavy beams and sliding Weights which operate satisfactorily as fixed installations but are objectionable in that they do not possess a desirable mobility nor are they capable of indi- 3O eating or recording rapid fluctuations of force. Such types are also incapable of accurately indicating relatively small weights or increments of force throughout a substantial range or capacity.

Modern research has demanded some type of distant-reading or distant controlled balance which shall be capable of applying the reaction to a given force in a location not accessible to an observer or under conditions where ordinary manual control of measuring apparatus would be impossible. Modern testing methods demand likewise a precision which requires that the effect of extraneous as well as inherent influences upon and of such a device be reduced to a negligible amount. vTo meet this demand, certain pressure operated types of instruments working in conjunction with manometers or gauges have been developed as have also certain electrical instruments, embodying in some shape or form, the simple electro-magnet, usually of the plunger type. These pressure operated and electrical clevices, however, sufler from the disadvantages that equilibrium at the distant point cannot always be assured and that the apparatus is not suited for accurate work on moving objects. 66

With the objects previously mentioned andthe limitations of the prior art in view, the automatically controlled distant-reading electroma netic balance about to be described was devised to meet the longstanding needs of engineering research which many have heretofore vainly sought to supply.

The balance proper consists essentially of two elements: an electro-magnetic device III which may exert a variable reaction to oppose the force W that may be substantially varied and which is applied to the balance, and a control device which maintains the balance automatically in equilibrium by adjusting the reaction, instantaneously and exactly, to correspond to the force applied with only a slight substantially constant frictional load thereon insufficient to detract from the accuracy of even quite delicate weighings. A wattmeter 30, which may or may not be recording, is used to indicate, either in watts or directly in units of weight, the magnitude of the widely variable force that may be applied.

The electromagnetic device III consists of a solenoid II with a core of magnetic material l2 producing a magnetic field in an air gap I3 in which there is mounted, by being wound about the periphery of a disc iii, a wire coil I4 of suitable shape, dimensions, and characteristics. This wire coil is mounted by suitable mechanical means I5 on a pair of flexible parallel springs I6, or other equivalent mounting, so that the coil may move back and forth in the magnetic field of the air gap, in a direction generally perpendicular to the lines of force, with negligible restraint and great accuracy and sensitiveness. The moving wire coil It in conjunction with its movable mounting I5 and I6 and associated parts will hereinafter be termed the active element.

When the solenoid I I is energized by a current, a powerful magnetic field is set up in the air gap I3 of a potency proportionate to such current. Upon a current being then passed through the moving coil I4, the conductors of this coil are acted on by a force parallel to the direction of its axis, in the line of the external force W applied to the balance but in the opposite direction. If the current in the solenoid I I is constant, or the lines of force in the air gap I3 are constant, the current in the moving coil I4, required to maintain the equilibrium of the balance, is proportional to the externally applied force W. The magnitude of the current in moving coil II is a measure of the force applied and by adjusting the current in coil I 4 automatically, the force tending to keep coil I4 within the magnetic field of. air gap I3 can be kept sensibly equal to the applied external force W, thus maintaining the balance in equilibrium.

Since the current in the moving coil ll of the active element is everywhere the same throughout the circuit in which it flows, its strength may be measured at any point in said circuit, however distant from the active element. Since the coil current is regulated by the voltage applied to this circuit and its total resistance, and since the voltage may be increased with the resistance to maintain the current constant in value under a certain reference condition of the balance, say no load, changes in temperature of the leads, varying contact resistance, and other similar factors do not affect the accuracy of the instrument.

This type of balance operates under the inherent disadvantage that the indicating current cannot be used as a direct measure of the force exerted unless the supply voltage to the main solenoid ll be held constant. Variations in this voltage will cause corresponding variations in the energizing current, in the'flux across the air gap II, and hence in the force exerted upon the active element, assuming a constant indicating current in the moving coil I4. However, as the flux varies closely as the impressed voltage on the main solenoid ll, indications of force applied to the balance may be registered with accuracy by the use of a wattmeter III which carries the main solenoid II supply voltage and the indicating current of moving coil I4 in its respective coils. It is understood that the wattmeter 30 instead of indicating watts, may be calibrated to read directly in pounds, ounces, or other indication of weight or force. Combinations of resistances, potentiometers, and ammeters may also be used for this purpose, either sight indicating or some preferred type of recording instrument.

If the balance is to remain in equilibrium under the influence of fluctuating loads, the indicating current must fluctuate directly in proportion with the load. It is obvious that with rapid fluctuations, manual control would become increasingly difficult with an increase in the rapidity of fluctuation until a point would soon be reached where manual control would be impracticable, if not impossible. To meet this problem, automatic control of the indicating current through the moving coil I4 is supplied and effected by mounting on the active element one half I! of a grid type shutter I0; the other half ID of the grid type shutter I! is flxed to the frame 2! of the apparatus. As the active element moves back and forth on its flexible practically frictionless spring mounting IS in the direction of its axis, the shutter is opened and closed. By using the grid type shutter, the total movement may be confined to narrow limits and may be adjusted at will by varying the position of the two halves I1 and ll of the grid type shutter with relation to each other.

The movement of the active element is restricted within rather narrow limits by the action of stops formed thereon, as shown in Fig. 2. One of these stops consists of a collar Iia formed near one end of the element adjacent the point where it passes through the frame 2|. The other consists of a centrally located abutment Iic formed on the other end of the element adjacent the end of core I2.

This limiting ofthe movement of the active element results in its movement taking place in practically a straight horizontal line throughout only a small arc of bending of the spring supporting elements I6. Throughout this small arc of bending the frictional stresses acting on the active element due to its suspension remain small and practically constant.

The mounting of the active element for limited movement in a horizontal direction has the advantage that the suspension members IB sustain all the weight thereof so that none of the opposing magnetic force is required to neutralize or counterbalance it, thus releasing all the opposing magnetic force for balancing the force to be measured.

Opposite the grid type shutter IS, on one side, is a source of light 2| and a suitable system of lenses 22 to focus and direct the light upon and through the shutter I9. Opposite the shutter I9, on the other side, is a light sensitive cell 23 acted upon by the varying amounts of light pasing through the shutter I 9 from light source 2|.

till

The light sensitive cell 23 is connected to the input 01 a vacuum tube amplifier in such manner that the amount oi light impinging upon the light sensitive cell 23 controls the amount of current passing through the moving coil ll of the active element which is connected in the output circuit of the amplifier. When the force applied to the balance increases, the active element moves and opens the shutter i9, allowing more light to impinge on the light sensitive cell 23. The current through the light sensitive cell 23 is increased and this increased current is amplified by means of amplifier 40 which results in an increased current in the moving coil i4. The increased current in moving coil it increases the force exerted by the active element and the balance again regains its equilibrium. Thus the variations of light through the shutter l9 cause corresponding variations in the current delivered by the amplifier 40 to the moving coil I4 which results in the external force applied and the reaction developed in the balance being held automatically in equilibrium.

ihe electrical connections of the light sensitive cell 23 and grid like resistor 24 across the input of the vacuum tube amplifier 40 is similar to that well known in the prior art as the typical direct current forward photo electric circuit wherein an increase of light at the photocell causes an increase in current across the cell which in turn eilectuates an increased current in the amplifier output circuit. The electrical characteristics of the associated circuits may be so adjusted by means of using various values for resistors 24, 25, and ii that the balance will respond practically in stantaneously to sudden changes in load, even to full range changes from no load to full load and vice versa, without hunting or unnecessary oscillation about the point of equilibrium. Fuses ill and 32 are provided for the protection of meter 39 and coils it and Hi. Overvoltage relay is provided to segregate the device from the source of potential 3% which may be any source of direct current at a potential of ill) volts or any other suitable voltage.

This type of balance can be hermetically sealed and adapted to the indication or recording of forces under water, such as when towing models of torpedoes, submarines, and similar objects submerged or it can be fitted with flexible diaphragms and used for indicating or recording the dynamic and hydrostatic pressures of liquids or gases in which it may be immersed. If desired, air gap l3 and the spaces surrounding the momabie coil may be filled with an inert gas, a fluid, or a vacuum, or other material having a constant magnetic pern ieability.

The device described lends itself readily to the measurement of forces at a point remotely located or inaccessible with respect to an operator. The wattmeter 30 may be located in any desirable position remote from the mechanical elemerits of the balance.

it will be understood that the above description and accompanying drawings comprehend only the general and preferred embodiment of my invention and that various changes in construction, proportion, and arrangement of parts may be made within the scope of the appended claims without sacrificing any of the advantages of my invention.

The invention herein described may bemanufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

What I claim as new and desire to secure by Letters Patent of the United States is:-

1. A force-measuring device comprising a support, a constant-field magnet having an annular air-gap carried thereby, a movable, annular coil disposed to move axially within said air-gap, a shaft restricted to motion of small amplitude and connected axially to said movable coil at one end thereof, parallel flexible means between said support and said shaft to permit axial movement of said shaft in such a manner that the weight of said shaft and movable coil will exert no substantial force on said movable coil and tending to so position it that said movable coil will be maintained in a predetermined location axially of said air-gap when the device is in neutral operating position and no force is being measured, a light valve grid mounted on said shaft between said parallel means, a parallel cooperating grid mounted on said support and means for connecting a means exerting a force to be measured axially at the other end or said shaft.

2. A. force-measuring device comprising a sup- 9 port, a constant-field magnet having an annular air-gap carried thereby, a movable annular coil disposed to move axially within said air-gap, a shaft restricted to motion of small amplitude and connected axially to said movable coil at one end thereof, parallel flexible, resilient members con-- necting said support and said shaft to permit axial movement of said shaft in such a manner that the weight of said shaft and said coil will exert no substantial force on said movable coil and tending to so position it that said movable coil will be maintained in a predetermined location axially of said air-gap against the action of external forces tending to move it therefrom, a light valve grid mounted on said shaft between said parallel means, a parallel cooperating grid mounted on said support and means for connecting a means exerting a force to be measured axlally at the other end of said shaft.

A iorce-rneasuring device comprising a support, a constant-iield magnet having an annular air-gap carried thereby, a movable, annular coil disposed to move axially within said air-gap, a shaft restricted to motion of small amplitude and connected axially to said movable coil at one end thereof, parallel spring members extending opposite directions from said shaft to said support to permit axial movement of said shaft in such a manner that the weight of said shaft and movable coll will exert no substantial force on said movable coil and tending to so position it that said movable coil will be maintained in a predetermined location axially of said air-gap when the device is in neutral operating position and no force is being measured, a light valve grid mounted. on said shaft between said parallel mem here, a parallel cooperating grid mounted on said support and means for connecting a means exerting a force to be measured, axially at the other end of said shaft.

4:. A force-measuring device comprising a support, a constant-field magnet having an annular air-gap carried thereby,-a movable annular coil carrying a variable current and disposed to move axially within said air-gap, a source of potential for said movable coil, a shaft restricted to motion of small amplitude and connected axially to said movable coil at one end thereof, parallel, flexible means between said support and said shaft to fill permit axial movement of said shaft in such a 7 manner that the weight of said shaft and movable coil will exert no substantial force on said movable coil and tending to so position it that said movable coil will be maintained in a predetermined location axially' of said air-gap when the device is in neutral operating position and no force is being measured, a light valve grid mounted on said shaft between said parallel means, a parallel cooperating grid mounted on said support and means for connecting a means exerting a force to be measured axially at the other end 01 said shaft, 21 current indicating instrument connected to indicate the current flowing through said movable coil, a light-sensitive cell connected to govern the magnitude of the current flowing in said movable coil, and a light source so positioned that said grids control the amount of light therefrom falling upon said lightsensitive cell.

5. A force-measuring device comprising a support, a constant-field magnet having an annular air-gap carried thereby, a movable annular coil carrying a variable current and disposed to move axially within said air-gap, a source of potential for said movable coil, an element restricted to motion of small amplitude for mechanically connecting said movable coil in opposition to the force to be measured, flexible spring-like members connected to said element at spaced points therealong, and to said support, and bearing the weight of said movable coil and said element and opposing within the limits of movement allowed said element any action by external forces to move said movable coil from apredetermined axial location within said air-gap, a current indicating instrument connected to indicate the current flow ing through said movable coil, a light-sensitive cell connected to govern the magnitude of the current flowing in said movable coil, a light source, and a grid-like screen mechanically associated with said element and movable thereby to control the amount of light from said light source falling upon said light-sensitive cell in proportion to the magnitude of the force acting on said connecting element.

SAMUEL E. DAWSON. 

